Changes in the collagen and glycosaminoglycan components of cervical connective tissue were studied in nonpregnant, intact pregnant, and ovariectomized hormone-treated pregnant rats. Collagen concentration and solubility and the concentration of the glycosaminoglycans dermatan sulfate (DS), heparan sulfate, and hyaluronic acid (HA) in cervices taken from day 9 (D9) pregnant rats were similar to those in cervices from nonpregnant rats. In cervical tissue from late pregnant intact control rats on D18 and D22, the collagen concentration decreased, collagen solubility increased, and there was no significant change in total glycosaminoglycan concentration. In cervices from ovariectomized pregnant rats treated with progesterone and estrogen, collagen and glycosaminoglycan parameters resembled those of D9 and nonpregnant cervices on both D18 and D22. However, treatment of ovariectomized pregnant rats with progesterone, estrogen, and porcine relaxin (R) restored cervical collagen concentrations to those of intact controls on both D18 and D22. On D18 of pregnancy, cervical collagen solubility was partially increased by R treatment, and by D22, it was similar to that of intact D22 pregnant controls. R treatment also resulted in a significantly increased cervical concentration of HA. It is concluded that the decrease in collagen concentration, increase in collagen solubility, and increase in HA concentration resulting from R action may contribute in part to the increased extensibility of the cervix that occurs during late pregnancy in the rat.